CoreXY Belt Drive

Design & Suppliers


As noted previously, in "A new anti-intersection iteration of the CoreXY principle design" at https://groups.google.com/forum/#!topic/h-bot-and-corexy-3d-printers/jR83iH8H2IM
and illustrated in the image posted there (and copied here) It's possible to avoid belt intersection issues in the Core-XY design by stacking the belts in a high (blue) and a low (red) belt path as shown.

the image links to a full size copy of the original image

This is a clever design that I want to incorporate into my modified UConduit printer.
The author of the above drawing is of the opinion that it does not matter if you use a smooth idler on the tooth side of the belt. However, SDP-SI has published a guide that recomends a pulley if one is available, or if smooth idler is used it should have a diameter of a 40 tooth pulley. See http://www.sdp-si.com/web/html/reference_library.htm and click on the D265 Technical section on Idler Usage or go directly to http://www.sdp-si.com/D265/HTML/D265T056.html. We searched for both drive pulleys and idler suppliers. Note: the pitch diameter of a 40 tooth 2mm GT2 pulley is 25.5 mm and the OD of a 40 tooth drive pulley is 25mm.

We also consulted the following internet threads:
idler pulley for GT2 belts - https://groups.google.com/forum/#!topic/bay-area-reprap/FYwrHvKGEdM
Toothed Idlers - love'em or hate'em - http://forums.reprap.org/read.php?1,184159,184210
Looking For A Source - Idler Pulleys - http://forums.parallax.com/showthread.php/154757-Looking-For-A-Source-Idler-Pulleys

To implement the design I'm going to need:
40 tooth Drive Pulley's (Q2)
Either 40 tooth Idler Pulleys or ~25mm Smooth Idler Pulleys (Q8)
2mm GT2 Drive Belt
Stepper Motors (q2)
Shoulder Bolts to mount the Idler Pulley's on
Spacers to position the Idlers on the Shoulder Bolts

Initial Design
This is a first pass at the belt drive design. I'm using the 25mm smooth idlers (ebay - chicobendavid) for the initial model. I've assumed the bearings are MR698ZZ (8x19x6). They are supplied with 5mm spacers. The single idler is a 16mm shoulder bolt with two 5mm spacers. The double idler is a 30mm shoulder bolt with two 5mm spacers (top/bot) and an 8mm spacer in between. Eventually I'll update it to use regular drive pulleys where the stepper motors should be (purple). The belt is assumed to be 2mm thick in this design, the backside idlers (orange) have been offset an additional 2mm to accomodate the belt thickness. The 4 corner mounts are fixed to the frame, the two green mounts are fixed to the XYcarriage.


Actual Construction
We are using the following components to assemble the idler pulleys
:
Pulleys
q8 xTIMING BELT IDLER PULLEY+BEARING, REPRAP 3D, DIY PRUSA, GT2, LINEAR MOTION
chicobendavid (Israel) - http://www.ebay.com/sch/chicobendavid/m.html - now offering q8/$45 + $5 ship -for $6.25 each!
8mm Shoulder Bolts
in both 16mm (single idler -q1) and 30mm (double idler & high single idler -q4) sizes.

http://www.boltdepot.com
Spacers
q10 - 5mm, q2 - 8mm, q2 - 19mm
K&S Round Aluminum Tube #9808 9mm OD x .45mm Wall (1) $2.09
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXBJXB&P=7


Making Your Own Spacers
Here's the process I used To cut my spacers from the aluminum tubing

Basic tools needed: Calipers, Marker for contrast (note the tubing has already been coated red), Knife or Scribe and Tubing Cutter.
I got mine used at a garage sale!
Since this is soft aluminum tubing you'll also need one of the shoulder bolts to keep the tubing from collapsing (see below).

Set the calipers to the size desired, use the lock (the knurled wheel on the top just above the mm/inch button) to hold the position.

Above: If you have a V-Block it will keep the tubing from rolling away while you scribe a cutting line.
Right: cutting line scribed with knife edge.

Above: scribed cutting line
Right: Line up the cutting wheel of the tubing cutter on the scribed line. Insert the bolt before starting the cut.


Tighten the cutter just a little with each revolution around the tubing

You should be able to see when the cut is complete.

Above: Loosen the cutter and remove
Right: Separate the parts. Notice the score mark on the shoulder bolt. It's mostly cosmetic.


GT2 Drive Pulleys
Since the Stepper Motors have 5mm shafts it would be good if the two drive pulleys have 5mm bores. Not allways easy to find...

SDP-SI - https://sdp-si.com/eStore/Catalog
A 6Z51M040DF0605 - 2 mm (GT2) Pitch,40 Teeth, 5mm Bore, Brass Insert, Polycarbonate Timing Pulley for 6mm Wide Belt $6.97
A 6A51M040DF0606 - 2 mm (GT2) Pitch,40 Teeth, 6mm Bore, 2 Flanges/With Hub, Aluminum Alloy Timing Pulley for 6mm Wide Belt $14.49
[note - 5mm bore not available in alu]

Powergrip GT2 Pulleys - Torque Transmission - http://www.torquetrans.com/gt2-pulleys

misumi - us.misumi-ec.com - GPA40GT2060-B-P6 - $19.50
High Torque Timing Pulleys - 2GT - 40 teeth 6mm bore

York - www.york-ind.com - TIMING BELT PULLEYS 2MM GT2 PITCH - note, bore in english units, .250 not 5mm!
Aluminum with Clear Anodize (RoHS compliant) For Belts Up To 6mm Wide

Boston Gear - no 2mm pulleys

Inventables - https://www.inventables.com/categories/frame-rail/pulleys - no 40 tooth pulleys

fivefive.co.ltd (china) - http://stores.ebay.com/fivefive-co-ltd
2pcs GT2 Timing Belt Pulleys 40T 10mm Bore for RepRap Prusa Mendel 3D Printer - 9.49 -  free ship
2pcs GT2 Timing Belt Pulleys 40T 5mm Bore for RepRap Prusa Mendel 3D Printer CNC - $9.49 (reg $9.99) - free ship
also sell bearings, timing belt (loops and open) and other reprap parts

WWX Electronics - wangwx2013 - http://stores.ebay.com/WWX-Electronics
5/6.35/8/10mm Bore 40 Teeth GT2 Timing Belt Pulley Stepper Motor 3D Printer - 5MM - $6.98 + $1.98 ship
also sells other reprap items - belt

GT2 Idler Pulleys (with teeth)
misumi - us.misumi-ec.com - gt2 40 tooth idler - AGTF40GT2060 - $25.14
Flanged Idlers with Teeth - P2M / P3M / P5M / P8M / 2GT / 3GT / 5GT / 8YU

GT2 Idler Pulleys (DIY with teeth)
GT2 Drive pulleys are available in large bore sizes (10mm). One thing I looked at was the option of cutting
off the hub from a drive pulley and installing bearings into it to make my own idler pulleys with teeth.

An MF105ZZ (10mm OD, 5mmID, flanged) or MF106ZZ (10mm OD, 6mmID, flanged) would work.
However, 10 pulleys are $62.69 when you add in the cost of  bearings (10/7.90)  the cost is almost $10/idler
(and that dosn't any allowance for the machining of the idlers)


GT2 Idler Pulleys (smooth)
Inventables -  https://www.inventables.com/categories/frame-rail/idlers - Idler OD - 17.5mm (not close enough to 25mm)

There are three eBay suppliers of smooth 25 mm GT2 idlers, both using the same drawings. Both supply bearings with 8mm ID.
smart-tools-4u (Israel) - http://www.ebay.com/sch/smart-tools-4u/m.html -
2 X TIMING BELT IDLER PULLEY + BEARING, REPRAP 3D PRINTER, DIY PRUSA,GT2,T2.5,T5 - $20.95 + 5.95 ship
diy-4u (Israel) - http://www.ebay.com/sch/diy-4u/m.html
TIMING BELT IDLER PULLEY, 3D PRINTERS, DIY, PRUSA, GT2,T2.5, LINEAR MOTION (inc shaft & spacer) 1/$9.95 + 5.95 ship
chicobendavid (Israel) - http://www.ebay.com/sch/chicobendavid/m.html
3 xTIMING BELT IDLER PULLEY+BEARING, REPRAP 3D, DIY PRUSA, GT2, LINEAR MOTION - q3/$19.95 + 3.95 ship +2.95 addl items
[buy 9 - total $69.70 or $8.72 for 8 with one surplus...]- now offering q8/$45 + $5 ship -for $6.25 each!

yellowvirtualsales - http://www.ebay.com/sch/yellowvirtualsales
2 Timing Belt Ball Bearing Roller Pulley Idler RepRap DIY 3D Printer GT2 T2.5 T5
but the OD of these is only 17.7mm (not close enough to 25mm)
note - supplier has other reprap items

3dtisk (Slovenia) - http://www.ebay.com/sch/3dtisk
6 X TIMING BELT IDLER PULLEY + BEARING, REPRAP 3D PRINTER, DIY PRUSA,GT2,T2.5,T5 - q6/$24.50 
+ 3.60 ship  or q4/$17.50 + 2.60 ship + $1.10 addl [assuming od is correct, buy 2x4 tot $38.70 - 4.84@]
no dimensions on Idler OD
note - supplier has other reprap items

GT2 Timing Belt

Fivefive.co.ltd (china) - http://stores.ebay.com/fivefive-co-ltd
Open End RepRap GT2 Timing Belt 6mm wide 2mm pitch 2GT for Pulley 3D Printer CNC 3.59/meter - free ship

WWX Electronics - wangwx2013 - http://stores.ebay.com/WWX-Electronics
New 1m GT2 Timing Belt Pitch 2mm Width 6mm 2GT Open Belt For Pulley 3D Printer - $4.99/meter + 1.98 ship

Stepper Motors
http://reprap.org/wiki/NEMA_17_Stepper_motor

The Kysan 1124090 seems to be the stepper motor of choice.
- Step angle: 1.8° (200 Steps per Revolution)
- Number of phase: 2
- 21 mm long, 5 mm Shaft -  D Cut
- Rated voltage: 4.2 V - Current / phase: 1.5 A
- Holding torque: 5.5 Kg-cm (54 N-cm, 76.4 Oz/in, 4.77 lb-in)
- Resistance / phase: 2.8 O ± 10%
- Inductance / phase: 4.8 Mh ± 20%
- Insulation resistance: 100 MO (500VDC)
- Kysan Electronics SKU:  1124090 - Mfg:  42BYGH4803-DC
- Operation temperature: -20°C ~ +40°C [is this a concern? steppers usually run hotter than this!]
drawing source - http://www.kysanelectronics.com/Products/datasheet_display.php?recordID=7850




sources
3dmakerworld - http://www.ebay.com/usr/3dmakerworld?_trksid=p2047675.l2559
$14.50 each + 13.85 ship (tot $86.35/5 motors)
biowavescom - http://www.ebay.com/usr/biowavescom?_trksid=p2047675.l2559
$80 + $15 ship (tot $95/5 motors )

Other Motors
NEMA 17 BIPOLAR STEPPER MOTOR 76 oz-in, KL17H248-15-4A
Shaft:  5mm diameter with flat, shaft length: 24mm
Current Per Phase 1.5A - Inductance: 4.8 mH -
Rated Voltage:  4.2V
Holding Torque:  5.5Kg.cm (76 oz-in)
automationtechsinc - http://www.ebay.com/usr/automationtechsinc?_trksid=p2047675.l2559
12.99 each + 17.85 shipping (82.80)

http://www.alltronics.com - OSM - NEMA17 Single Shaft 2A/83oz -  $18.25
http://www.phidgets.com/

Shoulder Bolts
While you can use just about any metric bolt as a shaft for the bearings, I prefer a shoulder bolt since it can be tightened down (to a precise height) on the shoulder.
It is, however, hard to find inexpensive shoulder bolts in sizes smaller than M6 (eg, M6 shaft, M5 thread)

Bolt Depot, Inc. - http://www.boltdepot.com
Metric shoulder bolts - http://www.boltdepot.com/Metric_shoulder_bolts.aspx?nv=l
Allen, Class 12.9 steel black oil finish
Shoulder Diameter6mm 8mm
Thread5mm x 0.86mm x 1.0
Thread Length9.7511.25
Head Diameter10 13
Head Height4.5 5.5
Shoulder Lengths10,12,16,20,25,30,40,5012,16,20,25,30,40,50,60,70
                 
Spacers
I'm going to use a tubing cutter and some thin wall tubing as spacers in the idler design.
While ready made spacers are available, these are cheap enough to do and can be adjusted to suit the precise size needed.

K & S Precision Metals - http://www.ksmetals.com/
Round Aluminum Tube http://www.ksmetals.com/23.html -  3906     7mm x .45mm x 1m
Round Brass Tubing - http://www.ksmetals.com/26.html -  9825     7mm x .45mm x 300mm

Tower Hobbies - http://www3.towerhobbies.com
K&S Round Aluminum Tube 7mm OD x .45mm Wall (2) - LXBJWZ - $2.69
Two 7 x .45mm Aluminum Tube - Length: 11.89" (302mm) - Diameter: 0.27" (7mm) - Hole Diameter: 0.24" (6mm)
K&S Round Brass Tube 7mm OD x .45mm Wall (2) - LXBJXM - $4.89
Two 7 x .45mm Round Brass Tubes -
Length: 11.9" (301.5mm)  - Outer Diameter: 0.27" (7mm) - Thickness: 0.018" (.45mm)


Contact Information
Contact me using: fpirz (at) media (dash) conversions (dot) net

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